1. Field of the Invention
The present invention relates to a compound semiconductor integrated circuit (IC) device, more particularly to a compound semiconductor IC device including bipolar transistors and field effect transistors (FET's).
2. Description of the Related Art
Silicon semiconductor devices have played a leading role in the development of microelectronics. Recently, however, compound semiconductor devices using a compound semiconductor such as gallium arsenic (GaAs), having a carrier mobility larger than that of silicon, have been developed in order to obtain increased operating speeds and decreased power consumptions over silicon semiconductor devices.
One of the main compound semiconductor transistors developed has been a compound semiconductor FET, due to, for example, the ease of the fabrication procedures. In particular, metal-semiconductor FET's (MESFET's) and junction-type FET's (JFET's) have been developed. A heterojunction type FET has also been proposed in which the carrier mobility is increased by isolating the region where the carriers (electrons) move from the region where the carriers are produced, thus eliminating any scattering of carriers by impurities doped to create the carriers.
With the recent advances in fabrication procedures, many compound semiconductor bipolar transistors have also been proposed. Particular promise is offered by heterojunction-type bipolar transistors, in which an emitter region and optionally a collector region consist of a compound semiconductor having a forbidden energy band gap larger than that of a base region. These allow independent control of flows of electrons and holes through the difference of the energy band gaps at the heterojunction interfaces, thus enabling increased electron injection efficiency and decreased emitter capacitance and base resistance.
In compound semiconductor devices, circuit integration has been tried but such compound semiconductor integrated circuit devices include only equivalent transistors and do not include both FET's and bipolar transistors. This limits the usefulness of compound semiconductor IC devices.